The present invention relates to a method for isolating and concentrating mixed-linkage beta-glucans from a beta-glucan source, such as cereal bran or grain, particularly oats and barley. The disclosed process is entirely aqueous and results in efficient production of beta-glucan concentrates. This is a divisional application of U.S. application Ser. No. 09/252,356 filed on Feb. 17, 1999.
Mixed-linkage (1xe2x86x923), (1xe2x86x924) beta-D-glucans, referred to herein as beta-glucan, are the predominant cell wall components of grain endosperm, particularly oats and barley, and are a well-established antihypercholesterolemic agent. In the case of beta-glucan found naturally in oats, this effect has been acknowledged by the U.S. Food and Drug Administration (FDA). Beta-glucan also has immunostimulatory properties when applied topically to the skin. The biochemical mechanisms by which beta-glucan exerts its therapeutic effects are largely unknown.
Cereal grain seeds generally contain a small amount of beta-glucan, with oats and barley being recognized as the richest sources of this material. The naked oat seed, known in the art as a xe2x80x9cgroatxe2x80x9d, typically contains from 2-4% by weight beta-glucan, depending upon oat variety and other factors such as growing conditions. Barley seeds may typically contain twice as much beta-glucan as groats. Beta-glucan is generally found in higher concentrations in the outermost layers of the seed (i.e., the xe2x80x9cbranxe2x80x9d). Thus, oat bran is defined as containing a minimum of 5.5% by weight beta-glucan, and typically contains up to 6% or 7% by weight beta-glucan.
In order to receive an efficacious amount of beta-glucan for reduction of low density lipoprotein (LDL) and total serum cholesterol, the FDA recommends total beta-glucan ingestion of at least 3 grams daily. However, it is difficult and inconvenient for the average individual to obtain this recommended amount because of the inherently low beta-glucan content in products such as oatmeal, oat bran muffins or cooked barley. For example, in the case of oatmeal, which is simply rolled whole oats, one would have to consume up to 150 grams (dry basis) each day, an amount which most individuals would find extremely burdensome. Accordingly, there is a compelling need to provide a more concentrated form of beta-glucan so that consumers can conveniently ingest therapeutic amounts of this material.
Previous processes for concentrating beta-glucan from cereals such as oats or barley have proven impractical for commercial manufacturing processes because of high cost and/or low yields. The prohibitive cost associated with processes disclosed in the literature is almost always a consequence of reliance upon a precipitation step in which beta-glucan is removed from aqueous solution by an organic solvent, especially alcohols such as ethanol or isopropanol, the use of which entails high in-process losses and difficult reclamation. This is evidenced in the marketplace wherein beta-glucan concentrates are only sold as cosmetic ingredients, with prices typically greater than $100 per pound. There is presently no concentrated form of beta-glucan priced so as to be affordable for use as a dietary supplement or food additive. The most concentrated form of commercially available beta-glucan for nutritional purposes contains just 15% beta-glucan (Nurtur(copyright) 1500, supplied by Nurture, Inc., Missoula, Mont.).
U.S. Pat. No. 5,518,710 to Bhatty discloses alkaline extraction of barley and oat bran, addition of an amylolytic agent to degrade starches, followed by precipitation of beta-glucan with a polar alcohol. Beer et al. (Cereal Chemistry 73:58-62, 1996) disclose a process for isolating beta-glucan in which oat bran concentrates are extracted in aqueous solution at alkaline pH, followed by dialysis, ultrafiltration or alcoholic precipitation. The material resulting from these processes had a beta-glucan content of about 60-65%. Westerlund et al. (Carbohydrate Polymers, 20:115-123, 1993) disclose a procedure for isolation of beta-glucan involving lipid extraction, enzymatic removal of starch and protein, and subsequent ethanol precipitation. EP 0 377 530 A2 discloses a process for the preparation of a beta-glucan-enriched grain for use as a food or food additive, in which oats are slurried in cold water, followed by rapid homogenization and screening of the slurry. U.S. Pat. No. 5,013,561 to Goering et al. discloses a process for recovery of various products, including beta-glucan, from barley. In this process, barley is milled, mixed with water, heated and centrifuged to remove insoluble material. The supernatant is then heated, and centrifuged to remove insoluble material, and the supernatant is subjected to ultrafiltration to remove soluble sugars and to concentrate beta-glucan solids.
There is a need for an entirely aqueous process for concentrating beta-glucan which is efficient, economical and produces highly palatable beta-glucan concentrates for use in foods and pharmaceutical formulations. The present invention addresses this need.
One embodiment of the present invention is a method for concentrating beta-glucan from a beta-glucan source, comprising the steps of: (a) providing an alkaline aqueous extract of the beta-glucan source; (b) acidifying or neutralizing the extract and heating the extract to between about 60xc2x0 C. and 100xc2x0 C.; (c) cooling the extract, whereby a flocculate is formed; (d) acidifying the cooled extract if the extract was neutralized in step (b); and (e) removing the flocculate from the extract to form an intermediate solution. Preferably, the beta-glucan source is cereal grain, cereal bran, milled cereal grain, milled cereal bran or distiller""s dried grain (DDG). Advantageously, the cereal is oats or barley.
In one aspect of this preferred embodiment, the aqueous alkaline extract has a pH of between about 7.5 and 12. Preferably, the aqueous alkaline extract has a pH of about 10. In another aspect of this preferred embodiment, the cereal grain is extracted at a temperature of between about 25xc2x0 C. and 80xc2x0 C. Advantageously, the extract of step (c) is cooled to between about 25 and 45xc2x0 C. In one aspect of this preferred embodiment, the flocculate is removed by centrifugation. In addition, an amylolytic enzyme may be added during step (b). The method may further comprise subjecting the intermediate solution to ultrafiltration. Preferably, the intermediate solution is heated prior to ultrafiltration. In one aspect of this preferred embodiment, the intermediate solution is subjected to diafiltration prior to the ultrafiltration step. In another aspect of this preferred embodiment, the intermediate solution is treated with activated carbon or ion exchange media. The method may further comprise the step of drying the intermediate solution. Preferably, the drying step is performed in a double drum dryer or spray dryer. The method may further comprise the step of heating the intermediate solution to allow evaporation therefrom, whereby a solid film or skin, enriched in beta-glucan, is formed on the surface of the solution. In addition, the method may further comprise the step of removing the beta-glucan film, resulting in formation of a second beta-glucan film. Preferably, the beta-glucan film removing step is performed one or more times. The method may further comprise drying the beta-glucan film. Another aspect of this preferred embodiment further comprises the step of subjecting the intermediate solution to ultrafiltration after removal of the beta-glucan film. Preferably, the ultrafiltration step removes salts and other contaminants from the intermediate solution.
Another embodiment of the present invention is substantially concentrated beta-glucan produced by the methods described above.
The present invention also provides an isolated beta-glucan enriched solid film or concentrate produced by the methods described above.
The present invention also provides a composition comprising beta-glucan produced by any of the methods described above, in combination with a food product.
The present invention also provides a pharmaceutical composition comprising beta-glucan produced by any of the methods described above, and a pharmaceutically acceptable carrier.
In addition, the present invention provides a cosmetic composition comprising beta-glucan produced by any of the methods described above.
Another embodiment of the present invention is an isolated beta-glucan-enriched film formed by evaporating a beta-glucan-containing solution until surface film formation occurs. The beta-glucan-enriched film may be provided in combination with a food product. The beta-glucan-enriched film may also be provided as a pharmaceutical composition in combination with a pharmaceutically acceptable carrier. The beta-glucan may also be provided as a cosmetic composition.
The present invention also provides a method for preparing concentrated beta-glucan by evaporating water from an aqueous beta-glucan-containing solution, and allowing a solid film of concentrated beta-glucan to form on the surface of the solution.